Preheat a pot to high heat.
Add the oil and sautée the chicken wings. They need to be really golden.
Remove the chicken wings and add the veggies. Make them golden as well. Use them to scrape any stuck bits of chicken from before.
Add the wings back in, add the water and decrease the heat to medium-low. Cover the pot. Let it simmer gently for 2 hours.
Use a spoon to remove the fat that floats on the stock.
Pass the stock through a colander and keep the stock only. We won't be using all of it so you can use the rest for soups, vegetable creams, stews, etc. You can also boil it down until you have a concentrated version of stock and freeze it to use later like it was a bouillon cube. With the vegetables from the stock, you can also make a vegetable cream.
Drizzle olive oil in a pan over medium-low heat. Add the onions and rosemary leaves and sauté them with patience. Let the onions go soft and sweet and then caramelize. Ideally, use a pan that you can pop in the oven afterwards.
Add the garlic and flour and cook for a minute.
Add the beer and sausages and increase the heat to high. Let the beer evaporate almost completely. Stir the contents every couple of minutes so it doesn't stick.
Add the stock and lay the mushrooms and cherry tomatoes on top.
Once the stock starts to boil take the pan to a preheated oven at 220°C / 430°F for 30-40min until the stock has thickened and the contents have become golden.
Serve hot with mashed potatoes and fresh rosemary.